Motor vehicle safety devices have continuously improved over the years and have made driving a safer experience. Many of these safety devices, such as seat belts and air bags are designed to protect occupants in the event of a crash. Other devices, such as anti-lock braking systems are intended to assist the driver's performance to prevent a crash. Such systems assume an alert driver, but this is not always the case. A driver may not be fully alert for any number of reasons. These include drowsiness, talking on a cellular phone, changing the radio stations and dealing with unruly children, for example.
A third category of safety devices includes those that detect the alertness of a driver. An example of a device that detects the alertness of a driver are vehicle monitoring systems that monitor the position of a steering wheel as the vehicle is driven. These systems are designed to recognize when the driver becomes drowsy based on detecting a period of time in which no steering adjustments are made. Alternatively, these systems may recognize when a driver becomes drowsy based on a steering adjustment whose speed exceeds a predetermined value over a relatively wide angle of steering.
These prior art monitoring systems that detect drowsiness operate on the raw steering angle data. A drawback with these monitoring systems is that they depend on the curvature profile of the road as well as the speed of the vehicle. Therefore these systems may be somewhat useful on straight lane driving, but are not useful in typical driving situations in which the road curvature profile varies.
Another drawback is that the prior art drowsiness monitoring systems do not consider situations where the driver is performing other tasks while driving. For example, such prior art systems do not recognize that the driver may be talking on the telephone or changing radio stations while driving. These prior art systems essentially perform a binary determination of whether a driver is drowsy based on the raw steering angle data and do not consider whether steering adjustments or lack of steering adjustments may be caused by factors other than drowsiness. Hence, these prior art systems do not correlate steering to a driver's secondary workload to generate a continuous index of driver workload.